We have previously reported that the postulated hepatotoxic metabolite of bromobenzene bromobenzene-3,4-oxide, can be detected in venous blood of rats trapping it as the corresponding [35S]-glutathione conjugates. Moreover, bromobenzene-3,4-oxide is detected in blood of rats treated with phenobarbital and diethyl maleate than in venous blood of rats treated with phenobarbital alone. The half-life of bromobenzene-3,4-oxide in blood is about 13.5 sec and it may therefore contribute to the extrahepatic covalent binding and toxicity observed after bromobenzene administration.